Gas turbines typically include a compressor, a combustor and a turbine. The compressor pressurizes air flowing into the turbine. Pressurized air is discharged from the compressor and flows to the combustor. Air entering the combustor is mixed with fuel and combusted. Gas turbine engines operate by combusting fuel with compressed air to create heated gases. The heated gases are used to drive a turbine for rotating a fan to provide air to the compressor. Additionally, the heated gases are used to drive a turbine to power the compressor. One type of compressor is made up of many alternating rows of rotating and stationary blades called rotors and stators, respectively. In this type of compressor, known as a multistage compressor, each successive rotor and stator pair is called a compressor stage. Each stage increases the pressure and density of the air.
In a multistage compressor, rotor blades push air past stator vanes at each stage. The rotor blades pressurize the incoming air. The rotor also adds swirl to the flow, increasing the total energy carried in the flow by increasing the angular momentum of the air. The stator removes swirl from the flow, but is not a moving blade so it cannot add any net energy to the flow. The stator vanes adjust the flow and direction of the gas passing through the compressor. Stators serve two purposes: the stators convert the kinetic energy of the air into pressure and the stators redirect the path of the air from the rotors to the next stage.
One way of achieving more efficient performance of the gas turbine engine over its speed range is to use variable stator vanes which can optimize the incidence of the airflow onto subsequent compressor stage rotors. The first stationary row, which is located in front of the rotor, is typically called the inlet guide vanes (IGV). The IGV adds no energy to the flow rather it is designed to add swirl in the direction of rotor motion to lower the Mach number of the flow relative to the rotor blades. The variable stator vane stages comprise a plurality of vanes capable of pivoting about an axis. A common device for controlling variable pitch vanes is a synchronization ring which surrounds the casing. A synchronization ring is axially spaced from the casing by centralizers which are disposed between the synchronization ring and the casing to provide support for the ring. The synchronization ring controls the vanes through a plurality of levers pivotally attached to the synchronization ring at a first end and to the vane at a second end, causing the vane to pivot about its axis when the ring is rotated. A large actuator, pivotally attached to the synchronization ring at a first end, provides the gross movement of the synchronization ring.
The force applied to the levers by the vanes opposes the motion of the ring. The centralizers also contribute some friction to the synchronization ring. These forces cause distortion of the synchronization ring resulting in vane angle error. One solution has been to stiffen the synchronization ring at the cost of additional weight. However it would be desirable to provide a method and system for correcting vane angle error by correcting synchronization ring distortion.
For the purposes of promoting an understanding of the principles of the embodiments, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the embodiments is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the embodiments as described herein are contemplated as would normally occur to one skilled in the art to which the embodiment relates.